As is well known, centering frames already known essentially consist of provisional structures made up of steel rods or of timber members with said structures being intendend for supporting arches and vaults during construction, and having extrados dummy boards on which the intrados of the arch structure to be built or restored is supported.
Among the centering frames already known, and more particularly among those which are not designed for large buildings, the movable and the stationary centering frames are to be distinguished. The first ones, as is well known, are employed when a set of identical structures are to be realized, or when a single structure can be made up by putting together the parts one after another, whereas the latter are to be partially or totally disassembled for being employed again.
Anyway, both the movable and the stationary centering frames already known are characterized in that they are to be completely or partially disassembled to adapt the same to different bending radii, as well as to the different load values and distributions.
Accordingly, one of the main drawbacks of the structures employed at the present time consists in the need for adapting and designing on each occasion the structure of the centering frame according to the kind of the desired bending.
Moreover, especially in the case of timber structures, the structures already designed and built according to some specified parameters can be hardly employed again for different solutions.
Stated in a schematic way, the structure of the centering frames adopted up to the present time in building technology is made up of a curved profile lattice set, and it is supported just at its sides, or it is possibly endowed also with intermediate supports, the whole structure resting directly on the ground or on the vertical bearing structures.
The assembling of such type of structure is generally difficult and requires the presence of skilled labor; in addition, such step must be necessarily carried out during installation.
A further drawback consists in the fact that, once the structure has been assembled, it is extremely difficult to substitute any possible defective parts.
Such drawbacks, especially if concerned with centering frame structures intended for restoration purposes in urban areas, affect at a remarkable extent both the progress of works and the cost of the restoration intervention.